In oil-flooded pumps, in particular rotary vane vacuum pumps, the pumping medium is directed through an oil separator on the delivery side of the pump in order to separate it from oil carried along with the medium and to recycle the oil into the oil bath. The oil separator is essentially formed by a set of filter cartridges which are disposed in a filter housing and through which the pumping medium flows. The filter cartridges need to be replaced at regular intervals. The filter housing has a housing cover or a special maintenance cover which can be removed after a few fastening screws have been unscrewed for providing access to the filter cartridges. Each filter cartridge is secured in the filter housing by a threaded plastic holder. Once the plastic holder has been released, the filter cartridge can be pulled out of the filter housing.